Precision parts or devices, such as light guiding panels, micro-needle arrays, micro-fluid channels, micro prism retroreflectors, lens arrays, etc., are used in the fields of optics, biotechnology, electronics, mechatronics and so on.
These precision parts are composed of structures of micrometer level or composed so as to have curved faces of micrometer level, which are required to have a surface roughness of nanometer level. Most of these parts are fabricated by molding of plastics or glass, so that dies for mass production of these parts are needed.
Machining of such dies requires an ultra-precision machine tool which is controlled to align a tool or workpiece with an accuracy of nanometer level. In the ultra-precision machine tool described in U.S. Pat. No. 6,870,286, a table or a machining head is driven in a non-contact manner with linear motors and aerostatic bearings, while the position of the table or the machining head is detected by a non-contact type linear encoder. Further, a pair of linear motors are disposed at the positions symmetric about the center of the table or the machining head and the table or the machining head is driven at equidistant positions from the center of mass, thus machining accuracy of nanometer level is attained,
However, the table or the machining head is disposed in an asymmetric manner about the machining point in the machine tool described in said USP, so that there is a fear that machining errors appear due to thermal displacement of the table or the machining head. Further, the length of the force loop between the tool and the workpiece is long because the machining head is supported on the column with an overhang, thus elastic deformation is accumulated in each portion and there appears errors of movement between the tool and the workpiece.